Oxygen metabolism release toxic products called free radicals which are implicated in many human diseases including autoimmune, ischemia/stroke, drug/toxin damage, atherosclerosis, arthritis, diabetes, ALS, aging, and cancer. Protection against free radical damage is provided by antioxidant enzymes including GSH-dependent enzymes. The cytosolic selenium-dependent glutathione peroxidase (GPXl) is one of the most important GSH-dependent protective enzymes. While detailed biochemical studies on GPXl regulation have been accomplished, little is known of regulatory control at a molecular level, notably in regard to induction of GPXl during stress. This proposal will investigate the regulation of GPXl by characterizing novel negative and positive regulatory elements in the flanking 5-nontranslated (5'NTR) or promoter region of the gene. Studies include DNA footprinting, nucleotide mutagenesis, and serial nucleotide deletion from 5'NTR GPXl/reporter chimeric constructs to identify nucleotides comprising the elements. The DNA-binding protein to the major oxidant-responsive element (ORE3) will be isolated. A novel element ORE4 is identified in the 5'UTR of GPX1 that may repress GPXl mRNA translation until oxidative stress occurs, similar to the iron-responsive element (IRE) in ferritin. Studies will determine the functional role of this element and its corresponding binding protein (ORE4-BP (previously isolated). The elements responsible for basal or core GPXl expression, as well as tissue-specific elements responsible for the unusual tissue expression of GPXl, will be identified. The mouse GPXl gene will be characterized to allow comparison to human GPXl in regards to basal, oxidative-responsive, and tissue-specific elements. These studies will provide critical information regarding cellular response to oxidative stress and aid in determining if a common regulatory mechanism exists for GSH-dependent enzymes.